1,1,2-trichloroethane dehydrochlorination

Scheme 17.3 1,1,2-Trichloroethane dehydrochlorination pathway involving an elimination with a carbocation formation. (Reprinted with permission from Ref. [SI]. Copyright 2000, Elsevier.)...

CH2 CCl2- Colourless liquid, b.p. 32°C, manufactured by the dehydrochlorination of trichloroethane. In the presence of light and air, it decomposes with the evolution of HCI, phosgene, and methanal and deposition of some polyvinylidene chloride. Consequently it must be stored away from light and in the presence of dissolved inhibitors (such as phenols and amines). Under the influence of... 

Dehydrochlorination of 1,1,2-trichloroethane [25323-89-1] produces vinyHdene chloride (1,1-dichloroethylene). Addition of hydrogen chloride to vinyHdene chloride in the presence of a Lewis acid, such as ferric chloride, generates 1,1,1-trichloroethane. Thermal chlorination of 1,2-dichloroethane is one route to commercial production of trichloroethylene and tetrachloroethylene. 

Dehydrochlorination of chlorinated derivatives such as 1,1,2-trichloroethane may be carried out with a variety of catalytic materials, including Lewis acids such as aluminum chloride. Refluxing 1,1,2-trichlorethane with aqueous calcium hydroxide or sodium hydroxide produces 1,1-dichloroethylene in good yields (22), although other bases such as magnesium hydroxide have been reported (23). Dehydrochlorination of the 1,1,1-trichloroethane isomer with catalytic amounts of a Lewis acid also yields 1,1-dichloroethylene. Other methods to dehydrochlorinate 1,1,1-trichloroethane include thermal dehydrochlorination (24) and by gas-phase reaction over an alumina catalyst or siUca catalyst (25). 

Dehydrochlorination of 1,1,2-trichloroethane at 500°C in the presence of a copper catalyst gives a different product, ie, cis- and /n7 j -l,2-dichloroethylene. Addition of small amounts of a chlorinating agent, such as chlorine, promotes radical dehydrochlorination in the gas phase through a disproportionation mechanism that results in loss of hydrogen chloride and formation of a double bond. The dehydrochlorination of 1,2-dichloroethane in the presence of chlorine, as shown in equations 19 and 20, is a typical example. 

Unreacted 1,1-dichloroethylene exits the reactor as vapor and can be condensed and recycled to the reactor. Product 1,1,1-trichloroethane exits the reactor as a Hquid, along with the Lewis acid catalyst, and can be removed from the catalyst by flash distillation. Selectivity is high however, some dehydrochlorination of the product can occur in the distillation step. 

Dehydrochlorination 1,1,2-Trichloroethane is easily dehydrochloriaated by a number of catalytic reagents to give 1,1-dichloroethylene and some 1,2-dichloroethylene. Refluxing with aqueous and methanolic solutions of NaOH, Ca(OH)2, and Mg(OH)2 and water gives 1,1-dichloroethylene... 

The rate of reaction is faster with the 1,1,2-trichloroethane than with 1,1,1-trichloroethane. Base-cataly2ed dehydrochlorination gives primarily... 

The monomer is produced from trichloroethane by dehydrochlorination Figure 17.2). This may be effected by pyrolysis at 400°C, by heating with lime or treatment with caustic soda. The trichlorethane itself may be obtained from ethylene, vinyl chloride or acetylene. 

Of the numerous reactions the most thoroughly studied is dehydrochlorination [12] (Scheme 2.3). Common dehydrochlorinating agents include alcoholic alkali [4], liquid ammonia [13], methylamine [13], LiCl in dimethylformamide (DMF) [14], MOH or M2CO3 (M = K or Na) in DMF [15] and tertiary and heterocyclic amines [16]. Moreover, some diaryltrichloroethanes, such as dichlordiphenyl-trichloroethane (DDT), may undergo thermal dehydrochlorination near 170-200 °C. 

Nitration of DDT and its dehydrochlorination product 1,1 -dichloro-2,2-di-(4-chlorophenyl)-ethylene led to the formation of bis(3-nitro-4-chlorophenylene) compounds containing 1,1,1-trichloroethane and carbonyl bridging groups [19,20]. These compounds were converted to the corresponding bis(3-amino-4-chlorophenylenes) l,l-dichloro-bis-(3-amino-4-chlorophenyl)-ethylene and 3,3 -diamino-4,4 -dichlorobenzophenone in accordance with Scheme 2.9 [5, 22, 24]. 

The point (a) is demonstrated by the data in Table 11 for 2-halobutanes which give three products 1-butene, cis-2-butene and frans-2-butene. The differences in selectivities can be even larger than indicated by these data. The dehydrochlorination of 1,1,2-trichloroethane yields 1,2-dichloro-ethylene (I) and trans- and ci s-l,2-dichloroethylene (II). On silica—alumina, the value of the ratio I/II was 10 3, on alumina, 0.30 and on KOH— Si02,10 [66]. 

The influence of temperature on the ratio of the products of the dehydrochlorination of 2-chlorobutane is seen from Fig. 6 [190], Other examples may be found in the literature [190,194,195]. Some ratios are almost temperature-independent while some show large changes. Moreover, the data from various sources differ sometimes appreciably (cf. refs. 190 and 914 for 2-chlorobutane and refs. 66 and 195 for 1,1,2-trichloroethane). This might be caused by secondary isomerisation on strongly acidic catalysts of the olefins first formed such a reaction was proved at... 

Another modification of the process can be used to meet the growing demand for 1,1,1-trichloroethane (methylchloroform). In this version, the chlorination of dichloroethane can be directed toward maximum production of 1,1,2-trichloroethane (9). This product when dehydrochlorinated yields vinylidene chloride, a widely used monomer. Hydrochlorination of vinylidene chloride yields 1,1,1-trichloroethane, a solvent of increasing importance. 

POLYVINYLIDENE CHLORIDE. [CAS 9002-86-2J. A stereoregular, thermoplastic polymer is produced by the free-radical chain polymerization of vinylidene chloride (H>C=CCIi) using suspension or emulsion techniques. The monomer lias a bp of 31.6°C and was first synthesized in 1838 by Regnault. who dehydrochlorinated 1,1.2-trichloroethane which he obtained by the chlorination of ethylene. The copolymer product has been produced under various names, including Saran. As shown by the following equation, the product, in production since the late 1930s, is produced by a reaction similar to that used by Regnault nearly a century earlier ... 

The most common commercial process for the manufacture of vinylidene chloride is the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess (2 to 10%). A continuous liquid-phase reaction at 98 to 99°C gives a 90 percent yield of vinylidene. 

Another, somewhat different process starts from 1,1,1-trichloroethane which after dehydrochlorination gives CFC142. The second step, dehydrochlorination of CFC142, is the same as above. The dehydrochlorination may be done either thermally or catalytically. At any rate, the production equipment has to be made from a highly corrosion-resistant material.52... 

Vinylidene chloride (VDC) is prepared commercially by the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess (2—10%) (3,9). A continuous liquid-phase reaction at 98—99°C yields 90% VDC. Caustic gives better results than lime. Vinylidene chloride is purified by washing with water, drying, and fractional distillation. It forms an azeotrope with 6 wt % methanol (10). Purification can be achieved by distillation of the azeotrope, followed by extraction of the methanol with water an inhibitor is usually added at this point. Commercial grades contain 200 ppm of the monomethyl ether of hydroquinone (MEHQ). Many other inhibitors for the polymerization of vinylidene chloride have been described in patents, but MEHQ is the one most often used. The inhibitor can be removed by distillation or by washing with 25 wt % aqueous caustic under an inert atmosphere at low temperatures. 

On the basis of the chemistry of chloral derivatives, one could suppose that transition from diacenaphthyltrichloroethane to the desired bis(naphthalic anhydride) can be carried out through oxidation of l,l,l-trichloro-2,2-bis(acenaphth-4-yl), subsequent anhydridization of pery-dicarboxylic groups, and dehydrochlorination of 1,1,1-trichloroethane moieties ... 

We recognize from previous discussions in Chapter 2 that 1,1,2-trichloroethane results from the base-catalyzed dehydrochlorination of 1,1,2,2-dichloroethane. From this analysis, however, we observe that there has been a change in the overall oxidation state of the carbon atoms in 1,2-dichloroethylene (0) compared to that of the parent compound (+ 2). We conclude that the formation of 1,2-dichloroethylene results from a process involving the transfer of two electrons. For larger, more complex molecules, we must only consider the atoms directly involved in the reaction process to determine if a change in oxidation state has occurred. 

Although the products of biotic and abiotic processes of this compound in the environment are adequately known, no systematic study is available that measured the concentrations of its reaction products in the environment. In instances where the product(s) of an environmental reaction is more toxic than the parent compound, it is important that the level of the reaction products in the environment be known. It is known that 1,1,2-trichloroethane under anaerobic conditions (e.g. in anaerobic soils leading to contamination to groundwater) may dehydrochlorinate to vinyl chloride (see Section 5.3), a compound more toxic than the parent compound. The analytical methods for the determination of the levels of these and other environmental degradation products of... 

Methyl chloride is used in the production of chlorosilanes which are intermediates in the production of silicone fluids, elastomers, and resins. Methylene chloride finds use in film processing, paint removing, metal cleaning, urethane foam blowing, and the electronic and pharmaceutical industries. Household food wraps such as Saran are made from VCM and vinylidene chloride. The latter is made by chlorinating EDC to 1,1,2-trichloroethane, followed by dehydrochlorination with caustic soda. 

Vinylidene chloride n, CH2 CCl2. A monomer. Bp, 37°C. A colorless, volatile liquid that is produced by the dehydrochlorination of 1,1,2-trichloroethane. It is a monomer for polyvinylidene chloride and is a comonomer with vinyl chloride (see saran) and other monomers such as acrylonitrile. (See image). 

In the first alternative, trichloroethane is prepared by the liquid phase chlorination of vinyl chloride at 30—SO C under pressure. In the second alternative, trichloroethane is obtained by liquid phase chlorination of ethylene dichloride at about 60°C in the presence of aluminium chloride as catalyst. The trichloroethane is then dehydrochlorinated by agitating with an aqueous suspension of calcium hydroxide at about 50 C, Crude vinylidene chloride distills off as it is formed and is then purified by distillation under pressure. The dehydrochlorination of trichloroethane may also be accomplished by heating at 400°C. Vinylidene chloride is a colourless liquid (b.p. 32" C). It is rather difficult material to handle since it readily polymerizes on standing. Polymerization occurs rapidly on exposure to air, water or light but even storage under an inert atmosphere does not completely prevent polymer formation. The monomer is therefore commonly inhibited with a phenol, such as p-methoxyphenol, which is removed by distillation or alkali-washing before polymerization. 

Dichloroethene is prepared mostly by the liquid-phase dehydrochlorination of 1,1,2-trichloroethane in the presence of alkali, e.g. NaOH... 

Dehydrohalogenation was also indicated to be catalyzed by acid-base pair sites. Table 3.18 shows the product distribution from dehydrochlorination of 1,1,2-trichloroethane over alumina as well as over silica-alumina (a typical solid acid) and KOH —Si02 (a typical solid base). Silica-alumina and KOH —Si02 showed products typical of acid and base catalysts, respectively. On the other hand, the products from alumina are different from the others and well explained by a concerted mechanism catalyzed by both acid and base. 

Vinylidene chloride dehydrochlorination 1,1,2-trichloroethane chloromethane, chloroethanes, chloroethylenes... 

Monomer, H2C=CCl2 (VDC), is a liquid (7), = 32°C) that is obtained by dehydrochlorination of 1,1,2-trichloroethane in the presence of soda. In spite of the steric hindrance brought about by two geminal chlorine atoms, this monomer polymerizes very easily by free radical process. In the absence of inhibitor, it polymerizes spontaneously during storage under the effect of atmospheric oxygen. 

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